The present invention relates to a differential piezoelectric actuator to be used in a disc drive, and more particularly, to the fabrication of a differential piezoelectric actuator.
Radial track density in disc drives continues to increase, resulting in an increased need for extremely precise head positioning systems. Voice coil motor (VCM) actuators are well-suited to effect coarse positioning, but lack the resolution to finely position and center a transducing head over a selected track. This inadequacy has led to a variety of proposals for a second stage microactuator to effect fine positioning in high track density disc drives.
The microactuator proposals have taken several forms, from an electrostatic microactuator attached to the slider carrying the transducing head, to a piezoelectric microactuator installed at the head suspension mounting block at a distal end of the actuator arm.
With respect to piezoelectric microactuators, there are currently two schemes for driving piezoelectric materials in secondary microactuators. The first is a single ended driving scheme where the piezoelectric material is attached with a conductive epoxy-solder paste to a stainless steel suspension which acts as the bottom electrode and electrical connection is made only to the top electrode. The second is a differential design driving scheme where the piezoelectric material is electrically isolated from the suspension and electrical connection is made to both the top and bottom electrodes of the piezoelectric element.
An advantage of the single ended design is its ease of manufacturing, as only one electrical connection to the small and fragile piezoelectric element is necessary. However, to maintain a class II UL listing, the voltage supplied to the piezoelectric element must be limited to +/xe2x88x9220 volts. Such a voltage is below that necessary to achieve the desired stroke. On the other hand, the differential design allows +/xe2x88x9240 volts to be supplied to the piezoelectric element which allows the desired stroke to be achieved. The differential design, however, complicates fabrication because electrical connection to both the top and bottom electrodes is needed. In addition, because the piezoelectric element is small and fragile, there is greater risk in the element becoming damaged during the fabrication process.
Thus, it is desirable to provide a fabrication process for a differential design that is simple and costs less than conventional processes of fabrication. In addition, it is desirable to provide a differential design that reduces the risk of damage to the piezoelectric element.
According to a first aspect of the invention, there is provided a method of fabricating piezoelectric elements each having a wrap-around electrode wherein the piezoelectric elements are formed from a sheet of piezoelectric substrate having a top electrode and a bottom electrode covering an entire top and bottom surfaces,respectively, of the substrate. The method includes the steps of:
(a) creating an isolation trench in the top electrode;
(b) exposing the substrate along a first direction to create exposed side surfaces of the substrate wherein the first direction is located remotely from the isolation trench;
(c) depositing an electrode on the exposed side surfaces of the substrate;
(d) exposing the substrate along a second direction to create second exposed side surfaces of the substrate wherein the second direction is locate remotely from the isolation trench on the opposite side of the isolation trench from the first direction wherein the first and second directions define each element""s length; and
(e) exposing the substrate along a third direction at multiple points on the substrate wherein defines each element""s width.
According to a second aspect of the invention, there is provided a method of fabricating a plurality of piezoelectric elements each having a wrap-around electrode wherein the process starts with a piezoelectric substrate having a top surface covered by a top electrode. The method includes the steps of:
(a) creating a discontinuity in the top electrode within a defined length for each piezoelectric element to be fabricated wherein the discontinuity divides the top electrode into a first top electrode and a second top electrode in each defined length;
(b) dicing through the top electrode and the substrate adjacent to each discontinuity to form an exposed side surface;
(c) depositing an electrode on the exposed side surface;
(d) dicing through the top electrode and the substrate substantially parallel to the dicing of step (b) but located remotely therefrom wherein the dicing steps (b) and (d) define a length of each element; and
(e) dicing through the top electrode and the substrate substantially perpendicularly to the dicing of steps (b) and (d) to define the width of each element.
According to a third aspect of the invention, there is provided a method of fabricating a plurality of piezoelectric elements each having a wrap-around electrode, wherein the process starts with a piezoelectric substrate having a top surface covered by a top electrode and a bottom surface covered by a bottom electrode. The method includes the steps of:
(a) creating a discontinuity in the top electrode within a defined length for each piezoelectric element to be fabricated;
(b) creating a via through the second top electrode wherein the via is electrically coupled to the bottom electrode;
(c) dicing through the top electrode, substrate and bottom electrode on each side of the vias to define each elements length; and
(d) dicing through the top electrode, substrate and bottom electrode in a direction perpendicular to the dicing of step (c) to define each elements width.